1. Field of the Invention
The present invention concerns hydraulic motors having axial pistons and an inclined cylinder head, also called drum motors.
2. Description of the Prior Art
Motors of this type are well known and, depending on their use, are supplied by various distributors. These take the form of either an "all or nothing" electrovalve or mechanically controlled valve for constant speed motors, or of an output regulator for variable speed motors. With servo movements, it is common to supply the motor through servovalves. On the other hand, protective elements must be combined with these to guard against over-pressure (i.e., safety valves) either in order to protect the motor itself or to limit its torque and protect the mechanism being driven.
When it is necessary to stop a driven inertial load, or to stop a drive load in case of the breakdown of the hydraulic supply system, the motor must be able to function as a pump, and therefore must be capable of being injected with a pressure of several bars by means of one-way injector valves. Furthermore, a shaft must often be available for driving a position, or motor speed, sensor. Finally, such a motor and its accessories must be connected to a hydraulic unit by four cahnnels:
a high pressure servovalve supply channel, a servovalve reservoir return channel, an injector channel and a hydraulic motor drain.
These four channels, and those required between the motor, the servovalve and the valves, make the unit large, heavy and costly. The size and weight are particularly prejudicial in applications where this equipment is packed onto moving machine units, e.g., on production robots.
Integration of valves within the cylinder heads of hydraulic machines is known. Fastening the servovalve directly onto the motor is also known. Lastly, connecting the motor drain to a servovalve return by placing special gaskets on the output shaft of the motor so as to ensure its seal despite the resulting over-pressure in the housing is also known. These improvements enable a reduction in the weight, volume and cost of the assembly, but are generally applied in isolation through the addition of separate elements, so that there exists no very compact complete unit.